1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a Metal-Oxide-Semiconductor (MOS) transistor and a method of fabricating the same.
2. Description of the Related Art
One technique that can be used to achieve high packing density in semiconductor devices is to shorten the length of gate channels in transistors. Shortening the channel length produces several problems such as short channel effect, minute pattern formation and restriction in operating speed. Of these problems, the short channel effect is the often the most serious problem. For example, it can increase the electrical field near the drain region and generate punchthrough, thereby causing a drain depletion region to penetrate into a potential barrier around a source region. Also, thermoelectron emission can incite avalanche breakdown and the resultant electrical field in a vertical direction decreases the mobility of carriers.
To solve the foregoing problems, a MOS transistor in which a channel protrudes in the vertical direction has been developed. A transistor having the protruded-shape channel is often referred to as a Fin Field Effect Transistor (FinFET). A FinFET can be manufactured by performing photolithography upon a Silicon-on-Insulator (SOI) substrate to form a fin which is the protruding portion. This done by photolithography upon a silicon substrate to form the fin, or by performing various other similar processes.
However, SOI may cause a floating body effect due to a lack of connection between a channel and the substrate, and it may degrade performance of the device due to lack of thermal conductivity. Furthermore, use of the SOI is much more expensive than the use of a silicon substrate. When the fin is fabricated by the photolithography, the narrow line width makes the patterning fastidious. Moreover, in such a process, the photolithography process is separately performed, and this results in further expenses.
The fin can also be fabricated using a wet etching method. However, when the fin is fabricated by wet etching, the vertical profile of the fin sometimes becomes inconsistent. That is, notching occurs in the fin or footing resulting from the widening of a lower end of the fin in contact with the substrate. In addition, undercutting occurs at both ends of the fin may occur.